FIG. 17 shows a transfer press 100 as a conventional press machine. As shown in FIG. 17, four uprights 121 are erected on a bed 123 located in a lower portion of a press frame 110 of the transfer press 100, and a crown 120 is provided above the uprights 121. A slide drive device is built into the crown 120 for driving a slide 122 disposed below the crown 120 so that the slide 122 moves upward and downward. Upper dies 112 are attached to a lower surface of the slide 122. Lower dies 113 are attached to an upper surface of a moving bolster 130 opposed to the slide 122, so that a work is press-formed by cooperation of the upper dies 112 with the lower dies 113. A pair of bars 114, 114 are provided on the right and left with the upper dies 112 and the lower dies 113 sandwiched therebetween, the pair of bars 114, 114 extending in parallel. The feed bars 114, 114 are provided with fingers (not shown) faced to each other for holding a work (not shown). By appropriately reciprocating the feed bars 114, 114 in a feed direction, a lift direction and a clamp direction, the work is sequentially transferred from the lower die 113 on an upstream side (the left side in FIG. 17) to the lower die 113 on a downstream side (the right side in FIG. 17). Incidentally, the feed direction means the direction in parallel with the work transfer direction, and motions in the feed direction include an advance motion (a motion from the upstream side toward the downstream side) and a return motion (a motion from the downstream side toward the upstream side). Further, the lift direction means vertical direction, and motions in the lift direction include a lift motion (a motion from the lower side to the upper side) and a down motion (a motion from the upper side to the lower side). Further, the clamp direction means a horizontal direction perpendicular to the feed direction (namely, the direction vertical to the paper surface in the FIG. 17), and motions in the clamp direction include a clamp motion (a motion for decreasing the distance between two feed bars 114) and a unclamp motion (a motion for increasing the distance between two feed bars 114).
Further, in the case of a three-dimensional transfer feeder, by repeating clamp operation, lift operation, advance operation, down operation, unclamp operation and return operation to the feed bar 114, the work is sequentially transferred to the lower die 113 on the downstream side.
A feed drive section 115 for moving the feed bar 114 in the feed direction is fixed on the lateral surface of the press frame 110 on the upstream side (or downstream side). A clamp drive section 116, which moves the feed bar 114 in the clamp direction, and a lift drive section 117, which moves the feed bar 114 in the lift direction, are provided on the bed 123 between the right and left uprights 121.
The feed drive section 115, the clamp drive section 116, and the lift drive section 117 respectively rotate a feed cam, a clamp cam and a lift cam with the rotating power fetched from a press main body, so that the feed bar 114 is driven by these cams to perform three-dimensional motion in the feed direction, the clamp direction, and the lift direction.
When performing die exchanging, the fingers also need to be changed so as to be suitable to the next dies. At this time, since the finger exchanging is performed by an external setup similar to the die exchanging, the fingers need to be mounted on the moving bolster 130 together with the feed bar 114 so as to be moved out from the work transferring area. The feed bars 114 can be split into a fixed part and a movable part, the fixed part being in a position to interfere with the uprights 121 while the feed bars 114 are being moved out from the work transferring area, the movable part capable of being mounted on the moving bolster 130 so as to be moved out from the work transferring area. When performing the die exchanging, the movable part is split from the fixed part, and only the movable part is moved out from the work transferring area along with the moving bolster 130 so as to perform the finger exchanging.
However, in the case of the movements in the feed direction, the clamp direction, and the lift direction are driven by the respective cams, to obtain a variable motion pattern of the feed bar 114, plural cams are needed according to the motion pattern, therefore not only the drive mechanism becomes complicated and expensive, but also the variable motion pattern is limited by the number of the cams. Thus recently there is a desire to easily obtain various motion patterns with a simple drive mechanism.
Thus a work transfer device is proposed, of which the feed drive section 115, the clamp drive section 116, and the lift drive section 117 are driven by respective servomotors, and the servomotors are controllable.
The feed drive section 115, the clamp drive sections 1 16, and the lift drive section 117, all these driving by means of servomotors, have the following configuration. The feed drive section 115 is provided with a ball screw mechanism, which uses a first servomotor as driving source, for reciprocating the feed bar 114 in the feed direction. The clamp drive section 116 is provided with a ball screw mechanism, which uses a second servomotor as driving source, for reciprocating the feed bar 114 in the clamp direction. The lift drive section 117 is provided with a rack and pinion mechanism, which uses a third servomotor as driving source, for reciprocating the feed bar 114 in the lift direction.
Further, as described in Patent Document 1, all of the feed operation, the clamp operation, and the lift operation of the feed bar also can be driven by linear motors. In such a work transfer device, the feed bar is suspended from a bracket fixed to the press main body. The linear motor is provided between the bracket and the feed bar, and the feed bar moves in the feed direction relative to the bracket so as to perform the feed operation. Also, the clamp operation and the lift operation are driven by respective linear motors provided on the lower surface of the feed bar.
Further, Patent Document 2 describes a work transfer device in which a fixed bar is provided with a first bracket which is driven by a linear motor so as to perform lift operation, the first bracket is provided with a second bracket which is driven by a linear motor so as to perform clamp operation, and the second bracket is provided with a third bracket with a work holder installed thereon, the third bracket being driven by a linear motor so as to perform feed operation.
Further, Patent Document 3 describes a work transfer device having a pair of lift beams arranged in parallel with the work transfer direction and capable of being freely moved in the vertical direction, a carrier provided on each lift beam and capable of being moved in the longitudinal direction of the lift beam by means of a linear motor, sub-carriers provided on the carrier and capable of being moved along a guide of the carrier in the carrier moving direction by means of a linear motor; and a cross bar spanning over the pair of oppositely facing sub-carriers and having a work holder. In such a work transfer device, the lift operation is performed by moving the lift beams by means of a servomotor. Further, the feed operation is performed by moving the carrier and the sub-carriers in the feed direction by means of a linear motor. Owing to the carrier and the sub-carriers, the moving range in the feed direction can be widened.
[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei10-314871 (Page 4 and FIG. 5)
[Patent Document 2] Japanese Patent Laid-Open Publication No. Hei11-104759 (Pages 2 to 3, FIG. 3, and FIG. 4)
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2003-205330 (Page 5 and FIG. 5)